A new high-altitude ballooning record

Liz: As some of you clever people have pointed out, the new Pi Zero with camera connector might have been designed with one person very much in mind. That person’s Dave “high-altitude ballooning” Akerman. We got one to him before they went on shelves so he could schedule a flight for launch day. Here’s Dave to tell you what happened (spoiler: he’s got another record for the highest amateur live-transmitted pictures). Thanks Dave!

As many reading this will know, I flew the new Pi Zero on the day it was announced, in order to test a prototype of our new PITS-Zero tracker board. I’d been pleading with Eben since I first saw a prototype of the original Pi Zero, that its low weight would be ideal for live-imaging HAB applications, if only it had a camera port. The camera is much the entire reason for using a Pi for HAB – if you don’t want pictures then a smaller/lighter/simpler AVR or PIC microcontroller will easily do the job (and with less battery power) – so I felt that the CSI-less Pi Zero was a missed opportunity. Eben agreed, and said he would try to make it happen.


So, when I received a sample Pi Zero with CSI port, I was keen to try it out. However launching an unreleased device, to possibly parachute down in front of a curious Pi fan, might not be the best idea in the world, so I had to wait. Fortunately the wind predictions were good for a balloon launch on the Pi Zero CSI launch day, and the flight went well albeit the burst was rather lower than predicted (balloons vary).

Sony Camera

I had hoped to fly the new Sony camera for the Pi, but in testing the camera would become invisible to raspistill after about 2 hours and roughly 2-300 photos. 2 hours isn’t long enough for a regular flight, and mine was expected to take more than 3 hours just to ascend, so this wasn’t good. I searched the Pi forum and found that a couple of people using time-lapse photography had found the same issue, and as it was a new issue with no fix or workaround yet, I had to opt for the Omnivision camera instead. This of course gave me a reason to fly the same tracker again as soon as there was a solution for the Sony firmware issue; once there was I tested it, and planned my next flight.

Waiting For Baudot

"It's currently a problem of access to gigabits through punybaud"

I’ve written previously about LoRa, but the key points about these Long Range Radio Modules when compared to the old (first used from the air in 1922) RTTY system are:

  • Higher data rates
  • Longer range with the same rate/power
  • Can receive as well as transmit
  • Low host CPU requirements even for receiving

The higher data rates mean that we can send larger images more quickly (throughput is up to 56 times that of 300 baud RTTY), and the receiving capability makes it easy to have the payload respond to messages sent up from the ground. For this flight, those messages are used to request the tracker to re-send any missing packets (ones that the receiving stations didn’t hear), thus reducing the number of annoying missing image sections down to about zero. To give you an idea of the improvement, the following single large picture was sent in about a quarter of the time taken by the inset picture (from my first Pi flight, and at the same pixel scale):



LCARS Chase Car Computer

For this flight, I tried out my new chase-car computer. This has a Pi B V2, Pi touchscreen, LoRa module, GPS receiver and WLAN (to connect to a MiFi in the chase car). The user interface mimics the Star Trek LCARS panels, and was written in Python with PyQt. It receives telemetry both locally (LoRa, or RTTY via a separate PC) and also from the central UKHAS server if connected via GSM.


The Flight

As per the previous Pi Zero flight, this was under a 1600g balloon filled with hydrogen. Predicted burst altitude was 42km, and I hoped that this time it might achieve that! The payload was the same as last time:


…except of course for the new Sony camera (manually focused for infinity, but not beyond) and a new set of batteries.

On the launch day the weather was overcast but forecast to improve a little, so I decided to wait for a gap in the clouds. When that came, the wind did too (that wasn’t forecast!), which made filling the balloon interesting.

No, my head hasn't turned into a giant clove of garlic.

No, my head hasn’t turned into a giant clove of garlic.

Fortunately, the wind did drop for launch, and the balloon ascended towards the gap I’d mentioned in the clouds:


The LoRa system worked well (especially once I remembered to enable the “missing packet re-send” software!), with the new camera acquitting itself well. I used ImageMagick onboard to apply some gamma to the images (to replace contrast lost in the atmosphere) and to provide a telemetry overlay, including this one, which I believe is the highest image sent down live from an amateur balloon.


Burst was a few metres later, comfortably beating my previous highest live-image flight.

And this was the last image it sent. I guessed why. Remember the camera stuck to the outside? My guess was that after burst – when the payload suddenly finds itself without support – the line up to the balloon found its way behind the camera which it then removed as the balloon remnants pulled on it. So, I can’t show you any images from the descent, but I can show you this shot of the Severn Estuary (processed to improve contrast) from the ascent:


In the chase car, I stopped at a point with a good view towards the landing area, so I could get the best (lowest) last position I could. With the payload transmitting both LoRa and RTTY, I had my LCARS Pi receiving the former, and a Yaesu 817 with laptop PC receiving the latter. With no images, the LoRa side dropped to sending telemetry only, which was handy as I was able to receive a lot of packets as the balloon descended. Overall LoRa seemed to be much more reliable from the car than RTTY did, despite the much higher data rate, and I now would be quite happy to chase a balloon transmitting high bandwidth LoRa and nothing else.

With the final position logged, I carefully tapped that into the car sat nav and then drove off to get the payload back. 10 minutes later I remembered that I’d coded exactly that function into my LCARS program! 2 screen-taps later, I had on-screen navigation (via Navit); I would also have had voice navigation but I hadn’t connected a speaker yet.

Both Navit and the car sat nav took me to a hill with the payload about 300 metres away. I waited for another HABber to arrive – his first time chasing – and meantime I updated the other enthusiasts online, and took some photographs of the scenery; Shropshire is very pretty.


Once Andy arrived, we walked down to the payload, watched (as often the case) by the local populace:

Ewe looking at me?

Ewe looking at me?

As expected, the camera was missing, so if anyone wants a free Sony Pi camera, I can give you a 5-mile radius area to search.


You don’t need CSI to see what went wrong here …

A lot of the balloon was still attached, which helps to explain how the camera was forcibly removed:


So, a nice flight and recovery. The Sony camera worked well; 868 LoRa worked well; the LCARS chase car tracker worked well. Next time, more duct tape!


karan avatar

Congratulations to dave on such an amazing feat!When will he release more information on the new tracker board?

David Akerman avatar

We decided to delay the zero-format tracker so we could improve it. The main change is that the layout has been completely reversed, so that the GPS is at the opposite end to the camera cable (we designed the board before the zero got a camera connector). It’s a good idea to keep the GPS and camera apart as video mode could potentially interfere with the GPS (I had this when using a long cable and the older camera).


karan avatar

Will you release the gerber files so that we can custom print the board or will you sell it?

David Akerman avatar

Once it’s on sale, we’ll release the gerbers, as we did for the existing board. That one is still in production and for some users will be a better option (it has a beefy power supply for those wanting to stack on the Astro Pi, APRS transmitter, etc.).

Wouter Rademaker avatar

Was there a special reason why the camera was stuck to the outside of the box?

Dave Akerman avatar

Easier than putting it on the inside, that’s all.

Niall Saunders avatar

Dave, or others, please correct me if I am wrong . . .

You said that you filled the baloon with ‘Hydrogen’? Surely not – did you mean Helium?

Also, one of your images shows you, a garlic-clove shaped baloon (replacing your head) and a rather suspicious Butane tank at your left hand. I assume that you have simply ‘decanted’ gas into this container – leaving me even more convinced that you wouldn’t be hessing around with hydroger, Hindenberg-style!


Liz Upton avatar

No, it’s hydrogen. (The Hindenberg disaster didn’t happen because of the hydrogen inside the balloon; the trouble was caused by the lacquer on the outside. It’s worth reading about; fascinating stuff. Sadly, in the popular imagination, hydrogen still gets the blame all these years later.)

echmain avatar

The fabric myth has long been debunked.


Hydrogen does what hydrogen does. Plain and simple.

David Akerman avatar

And in the confines of a balloon, with no oxygen, what it does is nothing.

Brandon F. avatar

Except slowly diffuse through the balloon membrane.

David Akerman avatar

Very, very, very slowly.

Unlike helium, which (as anyone who has seen a helium balloon deflate within a few days will know), hydrogen forms molecules so it diffuses much more slowly.


Nick Barnes avatar

Hydrogen burns, if introduced to oxygen. It doesn’t explode, which is why the Hindenburg didn’t explode. A hydrogen/oxygen mix explodes. Come on, surely we all did these experiment in school?

Barry Christian avatar

Only with a spark or some other ignition source.

David Akerman avatar

It’s a hydrogen tank – the new “Genie” style from BOC. These are much lighter than the old and very very heavy steel cylinders.

Niall Saunders avatar

Thanks for the clarification Dave (and Liz) – I stand corrected – and VERY far away!! It’s taken me the better part of forty years to grow back my eyelashes and, sadly, I wasn’t quite so successful with my hair.
That’s the risk of upscaling the little test-tube ‘squeak’ experiment from the chemistry lab – to a full-scale black bin-liner experiment in the playground (only fifty yards from the local police station)!
Dave – when are you going to add multiple baloons, and a small swing-seat for passengers?

Grant G avatar

Of course not! The hydrogen is perfectly safe if you have no oxygen to react with the hydrogen.

Gordon77 avatar

Well done !

I’m a bit baffled whether you used the Sony camera or not.

Looks like the old model in the photo of the box.

Dave Akerman avatar

I used the Sony. The pic was from the previous flight, as below the pic I explain that the payload was the same “except of course for the new Sony camera (manually focused for infinity, but not beyond) and a new set of batteries.”


zproxy avatar

cool. next send up a 360cam . and post it on yt. :)

rich avatar

Space next??? :)

David Akerman avatar

Astro Pi already did that!

Albeit inside a nice warm air-conditioned ISS :)

rich avatar

Ok, the moon? ;)

Dutch_Master avatar

Congrats on the record. Sadly, I think it’s safe to say that the Sony camera you lost will be of little use to anyone who finds it, if it had 40+km to reach terminal velocity :-\

Next stop, conquering the 50km limit?

JBeale avatar

Terminal velocity for small lightweight objects can be surprisingly small. Consider a leaf, for example. I think it’s possible the camera board could be OK, wherever it is- if not stepped on by some livestock!

Tom Archer avatar

I’m quite interested to know how you handle ‘littering’ of balloon pieces (and Pi parts!)

David Akerman avatar

In the vast majority of cases the whole thing is recovered, aside from balloon fragments (which can range from 1/3rd to almost all of the balloon). Those fragments are tiny and will decompose.

On 2 flights (and this was one of them) I’ve found and disposed of a party balloon in the field, so actually my hobby helps clean up the countryside :-)

Tom Archer avatar

Hi Dave that’s good to hear! A shame you haven’t been dropping Pi Zeros for people to find ;-)

Phil Norman avatar

Hi Dave…. Remarkable stuff. I am interested to know why the balloon ruptures. Is it the gas expansion or the low temperature?
If it is the gas expansion, couldn’t you hang a small diameter capillary tube from the balloon to a few metres under the gondola to prevent terminal pressure inside the balloon at altitude? Would you loose too much Hydrogen, or would it just never come back down?
Just a thought… Congratulations anyway.

Over-50 avatar

Whatever the gas, I find it really scary that the balloon appears to have been inflated beneath high voltage power cables.


David Akerman avatar

Why scary? What do you think would happen if non-conductive latex touched a power line?

Of course the balloon is secured to the cylinder during fill, and is carried well away from the lines for launch.

Over-50 avatar

I just want to encourage the next generation of engineers to work safely – that way they’ll have a chance to get old, grizzled and grumpy like me. With any luck they’ll also be much smarter than me, too.

Please, just take this as a comment to the wider and less experienced community that doing ‘stuff’ underneath power lines _can_ be a Really Bad Idea.

The power lines in the photo are (to my inexpert eye) probably ‘only’ 11,000 volts. The legal minimum ground clearance for 11kV distribution cables in the UK is 5.2m and the recommended minimum safety distance for those 11kV lines is 3m – so anything more than 2.2m off the ground risks infringing the recommended safety zone (also known as the “exclusion zone”). See http://www.hse.gov.uk/pubns/gs6.pdf pages 4 and 7, and its reference [2], particularly page 2, which also says “Please note that these are absolute minimum distances that should under no circumstances be infringed. If you do – it could prove fatal.”.

Yes, I know those publications are written from the viewpoint of contractors’ machinery but latex and string aren’t as non-conductive as one might expect when faced with such voltages (especially if there’s the slightest trace of dampness). As I’m sure you’re aware, contact with high voltages can really spoil your day.

“Safety rules are written in blood”.

Dave Akerman avatar

Understood. However the lines are over the field and I fill in the garden, so the lines aren’t above the balloon, whatever it looks like in the photos.

Phil Norman avatar

Hi Dave….. Remarkable pictures.
I am interested in why the balloon ruptures. Is it intentional?

Liz Upton avatar

Yes; as the pressure goes down, the gas in the balloon expands. At a certain height (depending on how much hydrogen is in the packet to start with) the balloon is expected to burst, and come down. It’s usually possible to make a reasonably good estimate of what that height is going to be; it can be quite a fine balance, taking into account the weight of the payload and the quality and weight of the latex as well as the amount of gas. (Some latex balloons are thicker or thinner than others; some have flaws…there’s a lot of variation.)

Luis Sebastián de los Angeles avatar

This article means SO MUCH for our high school HAB project. We are from Uruguay and we are drafting a HAB with environmental sensors as part of a year-long science project with students. The details you provide give us precious information about the how-to and what to expect up there. Thank you so much for sharing your experiences.

Dennis avatar

I’d like to point out that that altitude is just short of the distance of a marathon!


physicsgirl avatar

This is so cool! I dream of doing this and then trying it with my before and after school program here in the states. Thanks for sharing!

Sue Gray avatar

Well done Dave! Great photos and a record height too – fabulous. A truly compelling reason to work with Pi and Pi Zero. I’m sure the Skycademy Cadets 2015 salute you!

Tuomas Santakallio avatar

Actually hydrogen can be pretty safe even on high-payload dirigibles, if you put it inside lightweight capsules made of fireproofish material. Essentially, you have a glorified bubblewrap filled with the stuff. It doesn’t matter if a part of them light up, because the burn will be isolated. This kind of engineering makes a balloon of arbitrary size feasible.

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